In general, a motor rotor includes a rotary shaft having a magnet mounting portion, and a permanent magnet layer formed of a plurality of permanent magnets disposed on a surface of the magnet mounting portion. If the motor rotor rotates at a high speed, however, the plurality of permanent magnets may be broken by a centrifugal force. Then, Japanese Patent No. 2847756 proposes a motor rotor including a thread layer formed by winding a thread of a reinforced fiber material around the permanent magnet layer, first and second annular members provided on the rotary shaft and respectively disposed on both ends of the magnet mounting portion in the axial direction, and a cylindrical member fixed to the first and second annular members and in contact with a surface of the thread layer to cover it. The thread layer is impregnated with a curable resin. The first and second annular members and the cylindrical member are fixed by welding.    [Patent Document 1] Japanese Patent No. 2847756